Process for the continuous production of calcium-cyanamide



Aug. 31, 1954 2,687,945

-J. DANIELS PROCESS FOR THE CONTINUOUS PRODUCTION OF CALCIUM-CYANAMIDE Filed Sept. 18, 1950 INV ENT OR I 1172) .D aniels mx, 421%,, W

ATTORNEYS.

Patented Aug. 31, 1954 PROCESS FOR THE CONTINUOUS PRODUC- TION OF CALCIUM-CYANAMIDE Joseph Daniels, Essen, Germany Application September 18, 1950, Serial No. 185,454

Claims priority, application Germany September 22, 1949 4 Claims.

This invention relates to the production of calcium cyanamide by the reaction of calcium carbide with elementary nitrogen.

Calcium cyanamide has hitherto generally been manufactured from carbide by bringing the finely pulverised carbideif necessary with the admixture of a catalyst-into contact with nitrogen at high temperature in a mufile or a closed retort.

The pulverised carbide is for this purpose loosely poured into a container of iron or the like so that during the reaction it remains substantially at rest. As soon as the reaction has begun in one part of the material it gradually spreads throughout the entire contents of the vessel as the reaction is strongly exothermic.

It has also been proposed to keep the carbide moving during the action of the nitrogen. For example it has been proposed to sprinkle carbide in through the top of a vertical electrically heated blast furnace at the base of which gaseous nitrogen is introduced. These proposals have not however achieved practical significance.

The present invention comprises a process wherein pulverised calcium carbide is injected by means of a carrier gas into a reaction chamber at high temperature containing nitrogen, and is kept in suspension in the reaction chamber until the absorption of the nitrogen has substantially ended.

As carrier gases for the pulverised calcium carbide there may be chiefly considered nitrogen itself or a mixture of nitrogen with other gases, such as air. In each case the nitrogen may with advantage be preheated.

For carrying out the new process it is important to maintain continually within the reaction chamber a zone of sufliciently high temperature within which the carbide is brought to the temperature necessary for reaction with nitrogen, preferably 1200 or more. The maintenance of the said zone of increased temperature may be ensured in various ways.

It is for example possible according to the invention to introduce into the reaction chamber, in addition to the stream of calcium carbide and a carrier gas, combustible hydrocarbon gases and air.

According to the invention, a hydrocarbon gas itself may be used as a carrier gas in some circumstances.

The process may be carried out, for example, by introducing through a nozzle in an end wall of a reaction chamber, which may have the shape of a horizontal cylinder, a jet of hydrocarbon gas in which is suspended finely divided calcium carbide. In a preferred arrangement at the entry nozzle of the mixture an oxygen nozzle leads into the reaction chamber, so that the oxygen issuing from said nozzle immediately reacts with the combustible gas. In this way there is produced an inert flame of very high temperature which ensures the initiation of the reaction between carbide and nitrogen. The nitrogen is for this purpose introduced through suitable nozzles which are distributed around the entry of the carbide-gas stream and the oxygen.

Instead of the above method of operation the calcium carbide ma also be injected with nitrogen into the reaction chamber and entries for fuel gas and oxygen may be provided adjacent the nitrogen inlet.

Finally, it is also possible to supply the heat necessary for securing the reaction temperature either by the introduction of highly heated gaseous media, which consist of nitrogen or constituents which are inert in relation to the reaction to be carried out, for instance residual gas from the reaction chamber.

If combustible gases are empolyed to introduce the heat into the reaction chamber care must be taken that in their combustion the formation of carbon dioxide and water vapor is suppressed or is, in any event, only small.

If in this case coke oven gas is used as the fuel gas the combustion is carried out so that the hydrocarbons are converted substantially into carbon monoxide and hydrogen only. The combustion reaction is thus limited to the socalled non-luminous stage without resulting in the formation of substantial quantities of carbon dioxide and water vapor.

As the formation or" calcium cyanamide from carbide and nitrogen is a reversible process, it is preferable to provide means for preventing the temperature in the reaction chamber from exceeding a certain degree.

Several means for controlling the temperature in the reaction chamber are envisioned according to the invention. For example, there may be introduced into the reaction chamber gases of relativel low temperature which are heated in the reaction chamber by the exothermic reaction. By suitably determining the quantity tion chamber in the form of sensible heat of the gases. The hot gases can then be cooled outside the reaction chamber in any convenient manner, if necessary with the utilization of their sensible heat, such as for the production of steam.

Instead of this, or additionally thereto, the reaction chamber may be provided wholly or partly with a covering casing which may likewise be employed for the generation of steam, If necessary the cooling surfaces, may be movably arranged, such as in the form of a rotating cylinder, in order that reaction products deposited. on the cooling surfaces may be easily removed from the side turned away. from the reaction chamber, during rotation of the cooling. surfaces, by means of scrapers, or in any othersuitable way.

The temperature which is maintained in the reaction chamber depends upon the construction, namely the heat gradient which iecreated in the reaction chamber. Goodresults may be obtained with a temperature of about 1200 C. in the main reaction zone, but the temperature may also be kept higher if the reaction material 1 be quickly cooled. In. order to-initiate the reaction a temperature of 1000 to 1100? C. is usually sufficient.

The quantity of gaseous media which serves to inject the finely pulverised calcium carbide depends upon the grain size thereof. If the carbide is so finely ground that only 10%. remains on a sieve of 4900 mesh in a sieve test, a quantity of carrier gas of about 0.5 m9. isgenerally sufficient to inject 1 kg. of carbide into the reaction chamber in the form of a jet.

The nitrogen or a part thereof used inthereaction may be introduced in a highly preheated condition. Preferably heating up to. L000 to 1200 C. is employed.

In the reaction of calcium carbide with nitrogen elementary carbon is formed. This elementary carbon mixes as a soot with the cyanamide produced and-colours it gray to black;

In cases where it is required to remove deposited elementary carbon from the product, there may be additionally introducedinto the reaction chamber, a quantity of oxygen such that the elementary carbon is at least converted into carbon monoxide. It may be desirable in some cases to introduce the oxygen at a point removed from the main reaction zone.

In the accompanying drawing forming a part of this specification, there is shown for purposes of exempiification, a preferred form of apparatus in which the invention may be embodied and practised, without limiting the claimed invention specifically to the precise disclosure.

The figure shows a diagrammatic flow sheet partly in elevation and partly in vertical section of apparatus for carrying out the improvement provided by the present invention.

The apparatus shown in the figure comprises a reaction chamber I of refractory and non heat conducting brickwork Z. The reaction chamber I is tapered at its one end through which the reaction components enter. At the, opposite end the chamber is shaped as a discharged channel 3 being vertically arranged. At, the-smaller end of the reaction chamber I having the form of a truncated cone a nozzle I enters centrally and co-axially of the reaction chamber I., this nozzle being formed by a refractory pipe 5, The nozzle pipe 5 is connected to a regenerator 8 by means of a pipe I. This regenerator serves for preheating nitrogen that is fed from the feed lineB and that flows into the regenerator throughcheck valves 9 near the entrance to the regenerator. For heating up the regenerator 6 fuel gas (residual gas) is burnt in the upper freespaee fed from the feed line I0 through valves I I. The combustion air flows through feed-line I2 and valve I3 into the regenerator 6. The combustion products are vented from the regenerator 6 by valved line It connecting it to the stack flue (here not shown).

For heating the regenerator B the valves Ta and 2 are closed, whilst valves II, I3 and Illa are opened for introducing fuel gas and air into the regenerator respectively entraining combustion products, to the stack flue. The hot gases produced in the top part of the regenerator 6 flowed down through the refractory chequer filling of the regenerator 0 thus transferring their heat tothefilling. As soon as the temperature of the regenerator brickwork has been brought to the desired level the valves II, I3 and Ida are closed, and the nitrogen valves 9 and the connecting pipe valve i'a are opened.

The nozzle pipe 5 is surrounded by an annular channel at entering thereaction chamber I in form of an annular nozzle 22. This annular channel 2I is connected-to a mixing and blowing equipment 23 by means of pipe line 2 3'. Hydrocarbon gas from the valved feed line 25 is fed under suitable pressure into the mixing equipment 23. Furthermore, the end of a conve or screw 25 is connected to said mixing equipment 23, this screw conveying finely pulverised calcium carbide in adequate quantity to said equipment 23 from the storage bin 2?. The end of the conveyor screw 25 has the shape of a swivel 23 which rotates within the mixing equipment ztforming anannular slot 29 through which the finely pulverised solid stuff that is conveyed by the screw 26 is pressed out. When leaving the annular slot 29 the finely pulverised solid stuff is caught by the stream of the hydrocarbon gas being under increased pressure. This stream reaches the annular channel 32 that surrounds the slot-2 8 through the pipe line 3i. The channel 3% opens into the mixing equipment 23. This equipmenteifectsan intimate mixing of the linely pnlverised solidstuff with the hydrocarbon gas resulting in a practically homogeneous suspension. The mixture produced, having such a speed. that it cannot separate out, travels through pipe line 24 the annular channel 2 and through the nozzle 22 and is discharged into the reaction chamber I.

As is seen, an annular stream of city gas in which a finely pulverised sodium carbonate is suspended surrounds a middle zone in the reaction chamber I, this zone being formed by the stream of preheated nitrogen entering through the nozzle 4.

The annular channel 2i in the head of the reaction chamber I is surrounded by another annular nozzle arrangement 32 forming a similar shaped channel 33 in the nozzle head refractory material. The channel 33 is connected through valved line 34 to the feed-line 25 for hydrocarbon gas.

Finally, several separate oblique nozzles 35 enter the reaction chamber I, which are connected to the valved feed-line 36 for oxygen.

This arrangement of nozzles permits the introduction into the middle Zone of reaction chamber I of a fuel gas which reacts there .vith oxygen in an exothermic reaction so as to form a zone of higher temperature in the middle of the reaction chamber. The temperature in this middle zone will be regulated by suitable adjustment of the respective valves in such a way that the heat generated. is high enough to heat up by radiation and convection, to the necessary reaction temperature, the suspension of hydrocarbon gas and finely pulverised calcium carbide entering through the annular nozzle 22 and to assure a decomposition of the hydrocarbons entering the reaction chamber under formation of elementary carbon.

Instead of introducing a gaseous fuel through the nozzles 32 it is, in certain circumstances, also possible to apply a finely dispersed liquid fuel, e. g. fuel oil.

Oxygen from separate oblique nozzles 35 mixes with fuel gas from annular nozzle 32 and with hydrocarbon carrier gas from nozzle 22 so that when said mixture burns it produces arather high temperature, thus heating the suspended calcium carbide to such a degree Whereby the exothermic reaction with preheated nitrogen from central nozzle 4 may be carried out with a high yield of calcium cyanamide.

The media produced during the reaction in the reaction chamber I leave the chamber, as already mentioned, through the line 3. At the beginning of the outlet channel 3 a nozzle 31 is provided, which is controlled by the valve 38 and connected to the feed-line 39 for delivering cooled residual gas. This arrangement permits adding to the hot media in the channel '3 an adequate amount of cold residual gas and lowering suddenly the temperature of the reaction media. This temperature drop causes a certain amount of reaction products to separate, they gather at the bottom of the channel in a vertical extension and may be drawn off by the equipment 40.

If it is desired to remove deposited elementary carbon from the product, as previously indicated, oxygen may be introduced at a point removed from the main reaction zone as generally indicated at 53.

The other reaction media leave laterally through the opening M and enter, through the connection 92, a cooling chamber 43 fitted with water jacket 99. The cooling water enters the water jacket at 45 and is drawn off at 46. Then the reaction media descend the chamber 43. The solid components therein separate in part into the bottom part 47 wherefrom they may be drawn on by means of the equipment 48. The reaction media finally leave the cooler 43 in a pre-cooled condition through the pipe 49 leading to the dust separator (cyclone) 50 followed eventually by another cyclone (here not shown). In these two cyclones the rest of the recoverable solid stuffs is separated which then is drawn off by the equipment 5|.

The residual gas eventually flows, through pipe 52, to a final cooler (here not shown) where it is cooled down to a normal temperature level and drawn off for recirculating into line 39.

In the aforesaid specification, solid fuels (coal or the like) and gaseous fuels (fuel gas) are given as examples for the fuel that is applied in the process as per invention. It is, however, also possible to apply a fuel that is liquid in normal conditions as e. g. fuel oil. If such a liquid fuel is applied it should be advantageously finely dispersed or nebulized by means of a nebulizer or the like when entering the re action chamber and treated in a similar way as the fuel oil of so-called oil burners.

It may be observed that the process above described in an exemplification, though especially directed to the production of calcium cyanamide,

is not limited to this specific reaction, but may be used in all cases Where exothermic reactions between solid and gaseous media are to be performed, provided that solid or condensable products will result therefrom.

The process according to the invention is, apart from its employment in the production of calcium cyanamide, basically applicable to all exothermic reactions between solid and gaseous materials in which solid or condensable reaction products are formed.

Having thus described my invention with reference to a particular embodiment for carrying out the process according to my invention, it is to be understood that the invention is not limited to these particularities and that variation may be made within the limits of the invention as set forth above and in the appended claims.

What I claim is:

1. A process for the continuous production of calcium cyanamide by chemically reacting an elementary nitrogen with finely divided solid calcium carbide which comprises forming a homogeneous suspension of finely divided calcium carbide with a combustible hydrocarbon gas, blowing said suspension as a jet into a reaction zone maintained at a temperature which will effect reaction between calcium carbide and nitrogen, separately introducing oxygen and a gas containing elementary nitrogen heated to approximately reaction temperature into said reaction zone in the immediate neighborhood of the point of introduction of said suspension, the ratio of oxygen to combustible hydrocarbon gas being high enough to convert said hydrocarbon gas into carbon monoxide and hydrogen, and so maintain the high temperature necessary to cause the reaction between calcium carbide and nitrogen to occur, but insufiicient to cause the production of substantial quantities of carbon dioxide and water, maintaining the calcium carbide in suspension until the reaction is complete, cooling the reaction products and separating the calcium cyanamide so formed from the other reaction products and from the uncombined calcium carbide and recovering said calcium cyanamide.

2. A process as recited in claim 1 in which the oxygen and nitrogen are introduced in the form of preheated air.

3. A process as recited in claim 1 in which the reaction products are partly cooled within the said reaction zone.

4. A process as recited in claim 1 in which oxygen in addition to the amount of oxygen required to convert said hydrocarbon gas intocarbon monoxide and hydrogen is introduced into the reaction products at a point removed from said reaction zone in an amount sufficient to oxidize the elementary carbon obtained in the formation of calcium cyanamide to carbon monoxide.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 987,674 Frank Mar. 21, 1911 1,126,000 Fujiyama Jan. 26, 1915 1,212,504 Krauss et al. Jan. 16, 1917 1,230,343 Tommasi June 19, 1917 1,256,935 Sem Feb. 19, 1918 2,161,328 Winter et al. June 6, 1939 2,352,051 Wendlandt et al. June 20, 1944 

1. A PROCESS FOR THE CONTINUOUS PRODUCTION OF CALCIUM CYANAMIDE BY CHEMICALLY REACTING AN ELEMENTARY NITROGEN WITH FINELY DIVIDED SOLID CALCIUM CARBIDE WHICH COMPRISES FORMING A HOMOGENEOUS SUSPENSION OF FINELY DIVIDED CALCIUM CARBIDE WITH A COMBUSTIBLE HYDROCARBON GAS, BLOWING SAID SUSPENSION AS A JET INTO A REACTION ZONE MAINTAINED AT A TEMPERATURE WHICH WILL EFFECT REACTION BETWEEN CALCIUM CARBIDE AND NITROGEN, SEPARATELY INTRODUCING OXYGEN AND A GAS CONTAINING ELEMENTARY NITROGEN HEATED TO APPROXIMATELY REACTION TEMPERATURE INTO SAID REACTION ZONE IN THE IMMEDIATE NEIGHBORHOOD OF THE POINT OF INTRODUCTION OF SAID SUSPENSION, THE RATIO OF OXYGEN TO COMBUSTIBLE HYDROCARBON GAS BEING HIGH ENOUGH TO CONVERT SAID HYDROCARBON GAS INTO CARBON MONOXIDE AND HYDROGEN, AND SO MAINTAIN THE HIGH TEMPERATURE NECESSARY TO CAUSE THE REACTION BETWEEN CALCIUM CARBIDE AND NITROGEN TO OCCUR, BUT INSUFFICIENT TO CAUSE THE PRODUCTION OF SUBSTANTIAL QUANTITIES OF CARBON DIOXIDE AND WATER, MAINTAINING THE CALCIUM CARBIDE IN SUSPENSION UNTIL THE REACTION IS COMPLETE, COOLING THE REACTION PRODUCTS AND SEPARATING THE CALCIUM CYANAMIDE SO FORMED FROM THE OTHER REACTION PRODUCTS AND FROM THE UNCOMBINED CALCIUM CARBIDE AND RECOVERING SAID CALCIUM CYANAMIDE. 